Acrylonitrile polymer composition stabilized with metal formaldehyde sulfoxylate, formaldehyde, and acetic anhydride and method of making same



United States Patent Lloyd T. Jenkins, Decatur, Ala., and Richard R.Holmes, Bethesda, Md., assignors to The 'Chemstrand Corporation,Decatur, Ala., a corporation of Delaware No Drawing. Application May 23,1956 Serial No. 586,681

18 Claims. (Cl. 260-326) This invention relates to the stabilization ofacrylonitrile polymers and blends thereof. More particularly, it relatesto the stabilization of acrylonitrile polymers and blends thereof whichhave a tendency to develop color upon standing or application of heat.

The term polymer, as employed in the instant description and claims, isintended to include homopolymers, copolymers, and blends thereof, saidpolymers containing at least 80 percent by weight of polymerized orcopolymerized acrylonitrile in the polymer molecule.

Acrylonitrile polymers containing 80 percent or more of acrylonitrileare generally insolublein the more common solvents. In those instancesWhere suitable solvents have been found, in order to effect solution,the application of heat is usually necessary. Where heat is employed toeffect solutions, from which shaped articles are to be formed, a tan todark brown color frequently develops in the solutions and therefore iscarried over into the product formed therefrom. This color also developsin solutions upon standing for prolonged periods of time.

The mechanism which causes color formation has not been definitelyascertained, although a variety of reasons therefor have been advanced.The presence ofmetal ions, such as iron, copper and manganese in thesolutions may cause the color. The employment of amide compounds assolvents may result in formation of amines when heat is applied andcause color in the compositions. Impurities present in the solvents havealso been cited as a cause. {Whatever may be the reason forcolorformation, it results in compositions and products of undesirablestandards and therefore, has been the source of concern, particularly incommercial operations where such types of polymers or copolymers areemployed.

Accordingly, it is an objectof the present invention to preventundesirable color formation in acrylonitrile polymer compositions.Another object is to minimize color formation when solutions of theacrylonitrile polymers are permitted to stand for a prolonged period oftime or upon application of heat.

It is also an object of the invention to prevent color formation inacrylonitrile tures.

A still further object of the invention is the production of solutionsof acrylonitrile polymers and articles produced therefrom havingimproved color characteristics.

Other objects and advantages will be apparent from a consideration ofthe description of the invention which follows hereafter. i

In general, the objects of the invention are accomplished by dissolvingthe polymer of acrylonitrile in a suitable solvent therefor andpreventing or minimizing color formation by the presence in the solutionas an inhibiting agent, a combined reagent comprising an organic metalsulfoxylate, formaldehyde and acetic anhydride.

polymers at elevated tempera- 2,878,223 Patented Mar. 17, 1959 eralformula,

fl s R/ 0 M in whichR is an alkanol group containing 1 to 3 carbonatoms, an acyl group containing 1 to 3 carbonatoms or an aryl groupcontaining 6 to 8 carbon atoms, n is an integer from 1 to 2, and M issodium, potassium, zinc, etc. Compounds illustrative of this class aresodium formaldehyde sulfoxylate, zinc formaldehyde sulfoxylate,potassium formaldehyde sulfoxylate, zinc acetaldehyde sulfoxylate,sodium acetaldehyde sulfoxylate, potassium acetaldehyde sulfoxylate,zinc propionaldehyde sulfoxylate, sodium propionaldehyde sulfoxylate,potassium propionaldehyde sulfoxylate, etc.

The components of the inhibiting agent .may be 'employed in equal orunequal amounts, any one constituent being present in a range of from 98to 1 percent in a three componentsystem. The total amount of inhibitingagent may be employed in a range of about 0.3 to 15 percent, based onthe total polymer weight. However, it is preferred that the inhibitingagent of the instant invention be present in a small amount compared tothe amount of polymer dissolved. Thus, although the amount is notcritical, it is preferred that the inhibiting agent be present in theamount of about 0.3 to 3.0 percent, based on the total Weight of thepolymer. The inhibiting agent may be added to the solvents before orafter the polymer is dissolved therein. The inhibiting agent permitsexposure to high temperatures for prolonged standing periods without thedevelopment of the objectionable color which usually results in suchsolutions. The compositions of the instantinvention may be prepared in avarying temperature range. For example, the compositions of the instantinvention may be prepared by mixing the polymer, a suitable solvent andthe inhibiting agent at any temperature or heating the mixture to atemperature up to the boiling point of the solvent.

Among the solvents which may be used in practising the instant inventionare N,N-dimethylformarnide, N,N- dimethylacetamide, aqueous zincchloride, sulfuric acid, aqueous nitric acid, aqueous sodiumthiocyanate, ethylene carbonate, sulfolane, nitromethane, etc.

The polymeric materials, which may be employed in the practice of thepresent invention, are polyacrylonitrile, copolymers, including binaryand ternary polymers containing at least percent by weight ofacrylonitrile in the polymer molecule, or a blend comprisingpolyacrylonitrile or copolymers comprising acrylonitrile with from 2 to50 percent of another polymeric material, the blend having an overallpolymerized acrylonitrile content of at least 80 percent by weight.While the preferred polymers employed in the instant invention are thosecontaining at least 80 percent of acrylonitrile, generally recognized asthe fiber-forming acrylonitrile polymers, it will be understood that theinvention is likewise applicable to polymers containing less than 80percent acrylonitrile and the same stability is realized with theinhibiting agents defined herein. The acrylonitrile polymers containingless than 80 percent acrylonitrile are useful in forming films, coatingcompositions, molding operations,

monomers include acrylic, alpha-chloroacrylic and methacrylic acids; theacrylates, such as methylmethacrylate, ethylmethacrylate,butylmethacrylate, methoxymethyl methacrylate, beta-chloroethylmethacrylate, and the corresponding esters of acrylic andalpha-chloroacrylic acids; vinyl chloride, vinyl fluoride, vinylbromide, vinylidene chloride, l-chloro-l-bromo-ethylene;methacrylonitrile; acrylamide and methacrylamide;alpha-chloroacrylamide, r monoalkyl substitution products thereof;methyl vinyl ketone; vinyl carboxylates, such as vinyl acetate, vinylchloroacetate, vinyl propionate, and vinyl stearate; N- vinylimides,such as N-vinylphthalimide and N-vinylsuccinimide; methylene malonicesters; itaconic acid and itaconic ester; N-vinylcarbazole; vinylfurane; alkyl vinyl esters; vinyl sulfonic acid; ethylene alpha,beta-dicarboxylic acids or their anhydrides or derivatives, such asdiethylcitraconate, diethylmesaconate, styrene, vinyl naphthalene;vinyl-substituted tertiary heterocyclic amines, such as thevinylpyridines and alkyl-substituted vinylpyridines, for example,Z-Vinylpyridine, 4-vinylpyridine, 2-

cent of acrylonitrile, from 1 to percent of a vinylpyridine or al-vinylimidazole, and from 1 to 18 percent of another substance, such asmethacrylonitrile or vinyl chloride.

The polymer may also be a blend of polyacrylonitrile or of a binaryinterpolymer of from 80 to 99' percent acrylonitrile and from 1 to 20percent of at least one other C=C containing substance with from 2 to 50percent of the weight of the blend of a copolymer of from 10 to 70percent of acrylonitrile and from 30 to 90 percent of at least one otherC=C containing polymerizable monomer. Preferably, when the polymericmaterial comprises a blend, it will be a blend of a copolymer of 90 to98 percent acrylonitrile and from 2 to 10 percent of anothermono-olefinic monomer, such as vinyl acetate, which is not receptive todyestuff, with a sufficient amount of a copolymer of from 10 to 70percent of acrylonitrile and from 30 to 90 percent of a vinylsubstitutedtertiary heterocyclic amine, such as vinylpyridine or l-vinylimidazole,to give a dyeable blend having an overall vinyl-substituted tertiaryheterocyclic amine content of from 2 to 10 percent, based on the weightof the blend.

The polymers, useful in the practice of the present invention, may beprepared by any conventional polymerization procedures, such as masspolymerization methods, solution polymerization methods, or aqueousemulsion procedures. However, the preferred practice utilizes suspensionpolymerization wherein the polymer is prepared in finely divided formfor immediate use in the fiber fabrication operations. The preferredsuspen- 'sion polymerization may utilize batch procedures, Whereinmonomers are charged with an aqueous medium containing the necessarycatalyst and dispersing agents. A more desirable method involves thesemi-continuous procedure in which the polymerization reactor containingthe aqueous medium is charged with the desired monomers and thecontinuous withdrawal of polymer may also be employed. 2'

The polymerization is. catalyzed by means of any water-soluble peroxycompound,- for example the potas-;

sium, ammonium and other'water-soluble salts of peroxy acids, sodiumperoxide, hydrogen peroxide, sodium perborate, the sodium salts of otherperoxy acids, and any other water-soluble compound containing a peroxygroup (O-O-). A wide variation in the quantity of peroxy compound ispossible. For example, from 0.1 to 3.0 percent by weight of thepolymerizable monomer may be used. The catalyst may be charged at theoutset of the reaction, or it may be added continuously or in incrementsthroughout the reaction for the purpose of maintaining a more uniformconcentration of catalyst in the reaction mass. The latter method ispreferred because it tends to make the resultant polymer more uniform inits chemical and physical properties.

Although the uniform distribution of the reactants throughout thereaction mass can be achieved by vigorous agitation, it is generallydesirable to promote the uniform distribution of reagents by using inertwetting agents, or emulsion stabilizers. Suitable reagents for thispurpose are the water-soluble salts of fatty acids, such as sodiumoleate and potassium stearate, mixtures of watersoluble fatty acidsalts, such as common soaps prepared by the saponification of animal andvegetable oils, the amino soapsfisuch as salts of triethanolamine anddodecylmethylamine, salts of rosin acids and mixtures thereof, thewater-soluble salts of half esters of sulfuric acid and long chainaliphatic alcohols, sulfonated hydrocarbons, such as alkyl arylsulfonates, and any other of a wide variety of wetting agents, which arein general organic compounds containing both hydrophobic and hydrophilicradicals. The quantity of emulsifying agents will depend upon theparticular agents selected, the ratio of monomer to be used, and theconditions of polymerization. In general, however, from 0.01 to 1.0percent by weight of the monomers may be employed.

The emulsion polymerizations are preferably conducted in glass orglass-lined vessels which are provided with a means for agitating thecontents. Generally, rotary stirring devices are the most effectivemeans of insuring the intimate contact of the reagents, but othermethods may be successfully employed, for example by rocking or tumblingthe reactors. The polymerization equipment generally used isconventional in the art and the adaptation of a particular type ofapparatus to the reaction contemplated is within the province of oneskilled in the art. The articles manufactured therefrom may be producedby well-known conventional methods, for example, the wet-spinning,dry-spinning and meltspinning methods for producing fibers. I

The following examples are illustrative rather than limitative and allparts, proportions and percentages are by weight unless otherwisespecified.

EXAMPLE I 7.5 grams of a polymer blend of 88 percent of a copolymercontaining 94 percent of acrylonitrile and 6 percent of vinyl acetateand 12 percent of a copolymer of 50 percent of acrylonitrile and 50percent of 2-methy1- 5-vinyl pyridine were added to 45 milliliters ofN,N- dimethylacetamide containing approximately 0.05 gram of titaniumdioxide. The mixture was stirred and heated to 70 C. It was then quicklycooled to room temperature and the color measured. This sample was usedas a control. The purity is set forth below. Subsequently, a like samplewas prepared but with 0.225 gram of a color inhibitor containing 0.075gram each of sodium formaldehyde sulfoxylate, formaldehyde and acetican- 7.5 grams of a copolymer containing 94 percent of acrylonitrile and6 percent of "vinyl acetate were added to 45 milliliters ofN,N-dimethylacetamide containing approximately 0.05 gram of titaniumdioxidepThemixture was stirred and heated for 35 minutes ati70 C. It wasthen quickly cooledto room temperature and the color measured. Thissample was used as a control. The purity is set forth below.Subsequently, a like sample was prepared but with 0.225 gram of aninhibiting agent containing 0.075 gram each of sodium formaldehydesulfoxylate, formaldehyde and acetic anhydride. The purity is set forthbelow.

Table II Inhibitor Percentage Purity Used Control 10. 2 SodiumFormaldehyde Sulfoxylate, Formaldehyde and Acetic Anhydride 3 9. 4

EXAMPLE III 7.5 grams of an acrylonitrile homopolymer were added to 45milliliters of N,N-dimethylacetamide containing approximately 0.05 gramof titanium dioxide. The 'mixture was stirred and heated for 50 minutesat 90 C. It was then quickly cooled to room temperature and the colormeasured. Thissample was used as a control. The purity of the controlsample is set forth below. sequently, a like sample was prepared butwith 0.225 gram of an inhibiting agent containing 0.075 gram each ofsodium formaldehyde sulfoxylate, formaldehyde and acetic anhydride. Thepurity is set forth below.

Table III Inhibitor Percentage Purity Used Control 8. 5 SodiumFormaldehyde Sulfoxylate, Formaldehyde and Acetic Anhydride 3 1. 8

The tests for color indicative of approaching whiteness used throughoutthe examples consist of measurements of purity as calculated from thetristimulus values determined on a General Electric spectrophometer bythe methods recommended by theStandard Observer and Coordinate System ofthe International Commission on Illumination, as fully set forth in theHandbook of Colorimetry published by The Technology Press, Massa'chusetts Institute of Technology in 1936.

The compositions of the instant invention present many advantages. Forexample, products formed from the polymer solutions of the instantinvention are free of objectionable color and therefore of greatercommercial value. In preparing the polymer solutions, heat may beapplied without the danger of color formation and the solutions, ifnecessary, may stand for prolonged periods and remain free of color. Theinhibiting agents are readily available and inexpensive. Therefore, nogreat increase in production cost is necessary. The compositionscontaining the inhibitors may be prepared without going through detailedand elaborate procedures that necessitate expensive changes in thedesign of the apparatus used to manufacture them.

It will be understood to those skilled in the art that many apparentlywidely different embodiments of this invention can be made withoutdeparting from the spirit and scope thereof. Accordingly, it is to beunderstood that this invention is not to be limited to the specificembodiments thereof except as defined in the appended claims.

We claim:

1. A new composition of matter comprising a polymer Subcontainingatleast percent of polymerized acrylonitrile and up to 20 percent ofanother polymerizable mono olefinic monomer copolymerizable. therewith,a solvent therefor, and an inhibiting agent containing substantiallyequal proportions by weight of a compound having the general formula,

X i R OM wherein R is an alkanol group containing 1 to 3 carbon atomsand having the. free valence on a carbon atom joined to the hydroxygroup, n is an integer from 1 to 2, and M is a metal selected from thegroup consisting of sodium, potassium and zinc; formaldehyde and aceticanhydride.

2. A new composition of matter as defined in claim 1 wherein the polymeris a copolymer containing from 80 to 98 percent of acryonitrile and from2 to 20 percent of another polymerizable mono-olefinic monomercopolymerizable therewith.

3. A new composition of matter as defined in claim 1 wherein the polymeris a blend of 80 to 99 percent of (A) a copolymer containing to 98percent of acrylonitrile and 2 to 10 percent, of vinyl acetate and l to20 percent of (B) a copolymer containing 10 to 70 percent ofacrylonitrile and 30 to 90 percent of Z-methyl- 5-vinyl pyridine.

4. A new composition of matter as defined. in claim 1 wherein thepolymer is polyacrylonitrile.

5. A new composition of matter as defined in claim 1 wherein thecompound is sodium formaldehyde sulfoxylate.

6. A new composition of matter as defined in claim 1 wherein thecompound is potassium formaldehyde sulfoxylate.

7. A new composition of matter as defined in claim 1 wherein thecompound is zinc formaldehyde sulfoxylate.

8. A new composition of matter as defined in claim 1 wherein the solventis N,N-dimethylacetamide.

9. A new composition of matter comprising: a polymer blend of (A) acopolymer containing 90 to 98 percent of acrylonitrile and 2 to 10percent of another polymerizable mono-olefinic monomer and (B) acopolymer containing 10 to 70 percent of acrylonitrile and 30 to 90percent of a vinyl substituted tertiary heterocyclic amine, said blendhaving an overall vinyl substituted tertiary heterocyclic amine contentof from 2 to 10 percent' based on the weight of the blend, a solventtherefor, and an inhibiting 'agent containing substantially equalproportions by weight of a compound having the general formula,

p S 1 R/ o -M J wherein R is an alkanol' group containing 1 to 3 carbonatoms and having the free valence on a carbon atom joined to the hydroxygroup, n is an integer from 1 to 2, and M is a metal selected from thegroup consisting of sodium, potassium and zinc; formaldehyde and aceticanhydride.

10. A new composition of matter comprising a co polymer containing 80 to98 percent of acrylonitrile and 2 to 20 percent of vinyl acetate, asolvent therefor, and 0.3 to 15 percent, based on the total weight ofthe polymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of a compound having thegeneral formula,

wherein R is an alkanol group containing 1 to 3 carbon atoms and havingthe free valence on a carbon atom joined to the hydroxygroup, n is aninteger from 1 to 2, and M is a metal selected from the group consistingof sodium, potassium and zinc; formaldehyde and acetic anhydride. 1

11. A new composition of matter comprising a polymer blend of 80 to 99percent of (A) a copolymer containing 90 to 98 percent of acrylonitrileand 2 to 10 percent of vinyl acetate and 1 to 20 percent of (B) acopolymer containing 10 to 70 percent of acrylonitrile and 30 to 90percent of 2-methyl-5-vinylpyridine, a solvent therefor, and 0.3 to 15percent, based on the total weight of the polymer, of an inhibitingagent, said inhibiting agent containing substantially equal proportionsby weight of a compound having the general formula,

l-n wherein R is an alkanol group containing 1 to 3 carbon atoms andhaving the free valence on a carbon atom joined to the hydroxy group, nis an integer from l'to 2, and M is a metal selected from the groupconsisting of sodium, potassium and zinc; formaldehyde and aceticanhydride.

12. A new composition of matter comprising a polymer containing at least80 percent of polymerized acrylonitrile and up to 20 percent of anotherpolymerizable mono-olefinic monomer copolymerizable therewith, a solventtherefor, and 0.3 to 15 percent, based on the total weight of thepolymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal" proportions by weight of a compound having thegeneral formula,

i R O-M i wherein R is an alkanol group containing 1 to 3 carbon atomsand having the free valence on a carbon atom joined to the hydroxygroup, n is an integer from 1 to 2, and M is a metal selected from thegroup consisting of sodium, potassium and zinc; formaldehyde and aceticanhydride.

13. A new composition of matter comprising polyacrylonitrile, a solventtherefor, and 0.3 to 15 percent, based on the total weight of thepolymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of a compound having thegeneral formula,

l n O- M n wherein R is an alkanol group containing 1 to 3 carbon atomsand having the free valence on a carbon atom 8 joined to the hydroxygroup, n is an integer from 1 to 2, and M is a metal selected from thegroup consisting of sodium, potassium and zinc; formaldehyde and aceticanhydride.

14. A method for preparing a new composition of matter comprising mixinga polymer containing at least 80 percent of polymerized acrylonitrileand up to 20 percent of another polymerizable mono-olefinic monomercopolymerizable therewith, a solvent therefor, and an inhibiting agentcontaining substantially equal proportions by weight of a compoundhaving the general Jn wherein R is an alkanol group containing 1 to 3carbon atoms and having the free valence on a carbon atom joined to thehydroxy group, n is an integer from 1 to -2, and M is a metal selectedfrom the group consisting of sodium, potassium and zinc; formaldehydeand acetic anhydride, and heating the mixture to form a homogeneoussolution.

15. The method as defined in claim 14 wherein the polymer is a copolymercontaining from 80 to 98 percent of acrylonitrile and from 2 to 20percent of another polymerizable mono-olefinic monomer copolymerizabletherewith. V

16. The method as defined in claim 14 wherein the polymer is a blend of80 to 99 percent of (A) a copolymer containing 90 to 98 percent ofacrylonitrile and 2 to 10 percent of vinyl acetateand 1 to 20 percent of(B) a copolymer containing 10 to percent of acrylonitrile and 30 to 90percent of 2-methyl-5-vinyl pyridine.

17. The method as defined in claim 14- wherein the polymer ispolyacrylonitrile.

18. A method for preparing a new composition of matter comprising mixinga polymer blend of to 99 percent of (A) a copolymer containing to 98percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to20 percent of (B) a copolymer containing 10 to 70 percent ofacrylonitrile and 30 to 90 percent of Z-nethyl-S-vinylpyridine, asolvent therefor, and 0.3 to 15 percent, based on the total weight ofthe polymer, of an inhibiting agent, said inhibiting agent containingsubstantially equal proportions by weight of sodium formaldehydesulfoxylate, formaldehyde and acetic anhydride, and heating the mixtureto a temperature in a range of 25 C. to the boiling point of the mixtureto form a homogeneous solution.

lieferences Cited in the file of this patent UNITED STATES PATENTS2,502,030 Scheiderbauer Mar. 28, 1950 FOREIGN PATENTS 1,027,445 FranceFeb. 18, 1953 UNITED STATES PATENT OFFICE Certificate of CorrectionPatent No. 2,878,223 March 17, 1959 Lloyd T. Jenkins et a1.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 7, lines 54: to 58 inclusive, the formula should appear as shownbelow instead of as in the patent:

S 3 o-m Signed and sealed this 28th day of J uly 1959.

Attest:

KARL H. 'AXLINE, ROBERT C. WATSON,

Attesting Oficer. Commissioner of Patents.

1. A NEW COMPOSITION OF MATTER COMPRISING A POLYMER CONTAINING AT LEAST80 PERCENT OF POLYMERIZED ACRYLONITRILE AND UP TO 20 PERCENT OF ANOTHERPOLYMERIZABLE MONOOLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, A SOLVENTTHEREFOR, AND AN INHIBITING AGENT CONTAINING SUBSTANTIALLY EQUALPROPORTIONS BY WEIGHT OF A COMPOUND HAVING THE GENERAL FORMULA,